Synthesis methods of optically active β-amino acid have been introduced in, for example, Review and the like such as Tetrahedron, 1994, 50, 9517-9582, Chem. Soc. Rev., 1996, 117-128 and the like. Of these, an asymmetric 1,4-addition reaction of amine to α,β-unsaturated ester or amide (hereinafter sometimes to be abbreviated as α,β-unsaturated ester and the like) is a method attracting the highest attention because of the small number of reaction steps and easy availability of the starting materials. As a method for introducing asymmetry into the 1,4-addition reaction of amine to α,β-unsaturated ester and the like, there are three kinds of methods: i) a method using an optically active α,β-unsaturated ester or amide, ii) a method using an optically active amine and iii) a method using an asymmetric catalyst. Since the methods of i) and ii) are associated with difficulty in preparing an optically active form of a substrate, the development of the asymmetric catalytic method of iii) has been desired. The methods of iii) heretofore known include a method using alkoxyamine as an amine source (e.g., J. Am. Chem. Soc., 1998, 120, 6615-6616), a method using arylamine as an amine source (e.g., Chem. Commun. 2001, 1240-1241) and the like.
However, these methods have difficulty in finally leading to β-amino acid. In addition, the method using azide as an amine source (e.g., J. Am. Chem. Soc., 1999, 121, 8959-8960) has a problem in the safety of azide compound. Furthermore, a method wherein benzylamine, which is safe and easy to finally introduce into β-amino acid, is used as an amine source and an optically active β-amino acid is introduced by the asymmetric catalytic method has been reported in Org. Lett., 2001, 3, 389-392. This method, however, requires use of a polymer compound, which is not easy to prepare, as an asymmetric catalyst, and is not entirely satisfactory.